Abstract: A coolant sub-assembly is provided for use in a DNP apparatus. The sub-assembly comprises a plurality of concentric jackets surrounding an inner bore tube having first and second opposed ends. The jackets are adapted to inhibit heat flow to the inner bore tube, a DNP working region being defined within the inner bore tube where a DNP process will be performed on a sample in the DNP working region. A coolant supply path extends adjacent an outer surface of the inner bore tube at the DNP working region in order to cool said outer surface, whereby a sample holder assembly can be inserted through the first end of the inner bore tube to bring a sample holder into the DNP working region and can be moved through the second end of the inner bore tube. An auxiliary coolant supply path supplies coolant to a sample, located in use in the sample holder at the DNP working region, through at least one aperture in the inner bore tube wall at the DNP working region.

Abstract: A coolant sub-assembly is provided for use in a DNP apparatus. The sub-assembly comprises a plurality of concentric jackets surrounding an inner bore tube having first and second opposed ends. The jackets are adapted to inhibit heat flow to the inner bore tube, a DNP working region being defined within the inner bore tube where a DNP process will be performed on a sample in the DNP working region. A coolant supply path extends adjacent an outer surface of the inner bore tube at the DNP working region in order to cool said outer surface, whereby a sample holder assembly can be inserted through the first end of the inner bore tube to bring a sample holder into the DNP working region and can be moved through the second end of the inner bore tube. An auxiliary coolant supply path supplies coolant to a sample, located in use in the sample holder at the DNP working region, through at least one aperture in the inner bore tube wall at the DNP working region.

Abstract: A refrigerator for cooling a sample (16,17) comprising a reservoir (1) for storing gaseous .sup.4 He when in use; a cooler (13) for cooling gaseous .sup.4 He from the reservoir; and a helium vessel (18,19) for containing .sup.4 He, the .sup.4 He in the helium vessel being in fluid communication with the reservoir (1) via the cooler (13). The sample (16,17) is mounted, in use, in thermal contact with the .sup.4 He in the helium vessel whereby the .sup.4 He in the helium vessel provides a path for heat to transfer from the sample to the cooler.